Article written by: Heather Alexander

1. The Earth was the centre of the solar system

Copernicus’s schematic diagram of his heliocentric theory of the Solar System from De revolutionibus orbium coelestium

Geocentricism, those were the good old days, back when we thought everything revolved around us! Under the geocentric model, we believed that everything, from the Sun, to the moon, planets and stars, all revolved around the Earth. This sounds preposterous to us now, however we were convinced of this right up until Nicolaus Copernicus came up with the idea that the Earth actually orbited around the Sun instead. He came up with this new found theory in 1543 and back then this was a revolutionary idea. It wasn’t accepted until the 1600s, when Johannes Kepler published his famous “Laws of Motion,” which supported the heliocentric model.

2. The planets and stars were all on different shells that surrounded the Earth

We used to believe in Celestial Spheres. This idea sort of goes along with the geocentric model. Astronomers in ancient Greece used to believe that the Sun, Moon, Planets and Stars were all positioned in their own “shells” that surrounded the Earth. In these celestial models, the apparent motions of the fixed stars and planets are accounted for by treating them as “embedded” in rotating spheres. Since it was believed that the fixed stars did not change their positions relative to one another, it was argued that they must be on the surface of a single starry sphere. When something was observed that couldn’t be explained fully by the model, another celestial sphere was added to the mix.

3. We were terrified of Solar Eclipses

You may argue that some people are still terrified of a solar eclipse today, however this is really nothing when you compare it to the fear people had centuries ago! You have to remember that the Sun was a massive part of certain cultures, like the Inca and Aztecs, and when something happened to the Sun that couldn’t be explained, their fear and outrage caused them to do terrible things, normally along the lines of human sacrifice. Other cultures believed the Sun was being eaten by a demon or a dragon and they would bang pots and other noisy things to scare the creatures off. Thankfully now we understand that a solar eclipse is simply the passing of the moon in front of the Sun, casting its shadow on the Earth.

4. There were only nine planets that existed

Exoplanets galore! This artist’s concept shows what each of the TRAPPIST-1 planets may look like, based on available data about their sizes, masses and orbital distances. Image Credits: NASA/JPL-Caltech

Once upon a time, we didn’t know that there were exoplanets! We believed that our solar system had the only planets in the galaxy. Thankfully we discovered our first exoplanet in January 1992. These first exoplanets were discovered orbiting around the pulsar known as PSR 1257+12 by Aleksander Wolszczan and Dale Frail. The first exoplanet discovered orbiting around a star similar to our Sun was found in the constellation of Pegasus, orbiting around 51 Pegasi B. There are now nearly 4,000 exo-planets known, as catalogued in this list.

5. Pluto is a Planet

The first proper image was Pluto was first taken in July 2015. Credit: NASA

Technically Pluto is now a Dwarf Planet, but will we ever fully accept that? Pluto was discovered back in 1930 by Clyde Tombaugh. Back in 2006 the IAU decided that it was a great idea to downgrade Pluto and this royally messed with all the people who had, for years, been taught that Pluto was a planet. We love you Pluto, to certain generations of people, you will always be a planet! The International Astronomical Union’s resolution that redefined the status of Pluto, during its XXVIth General Assembly in Prague in 2006, can be found here.

6. The Universe is slowing down

For a long time we believed that the expansion of the Universe was slowing down, but actually it is the opposite. The Universe is expanding faster than we thought. For every million parsecs of distance from the observer, the rate of expansion increases by about 67 kilometers per second. The rate of expansion is actually accelerating, not decreasing!

7. Mars had Canals

Nowadays we know that Mars definitely does not have canals, not in the sense that Giovanni Schiaparelli believed anyway. During the planet’s “Great Opposition” of 1877, he observed a dense network of linear structures on the surface of Mars which he called “canali” in Italian, meaning “channels” but the term was mistranslated into English as “canals.” These observations and mistranslations led on to the belief of life on Mars and it was believed that Mars had these canals right up to 1916. This also had a big impact on 20th century science fiction.

8. There were no other galaxies but our own

We humans seem to have been really keen on the idea that we were the complete centre of the universe and no one else and nothing else could possibly exist. Thanks however to Edwin Hubble, we now know that there is so much more to our universe than just us. Hubble discovered that many objects previously thought to be clouds of dust and gas, classified at the time as “nebulae”, were actually galaxies beyond the Milky Way. He later found a that the greater the distance of a galaxy away from us the faster it is moving away from us, on average. This recession is now known as the redshift, and the linear relation between velocity and distance as Hubble’s Law – one of the most famous discoveries in astronomy.

STOP PRESS: At the XXXth General Assembly of the International Astronomy in Vienna in August 1018 astronomers debated whether to change the name of the law to the Hubble-Lemaitre law to acknowledge the important role that George Lemaitre, a Belgian priest, played in this discovery. The decision will shortly be put to the members of the IAU – the professional astronomers of the world – for a vote. A straw poll conducted during the General Assembly suggested that there would be strong support for this motion.

9. Comets were bad omens

Looking fabulous: Comet ISON on the 8th Oct 2013 as seen through the 0.8m Schulman Telescope. Credit: Adam Block/Mount Lemmon Skycentre/University of Arizona

In the ancient times comets were believed to be bad omens. They were also known as “hairy stars!” You can understand why the ancient people feared them. They are beautiful to look at in the sky, but without the information we know about comets now, their looming presence in the night sky, and often the day time sky, was foreboding. The people viewed them as omens of impending catastrophes or the death of a King or nobleman. Halley’s comet was in the sky just before the Battle of Hastings in 1066 when William the Conquerer conquered England. Today we know Halley’s comet has an orbital period of 76 years, but back in 1066 this was just considered bad timing.

10. The Earth was flat

This is probably a controversial one as we all know there is a healthy dose of people who still believe that the Earth is actually flat. Thousands of years ago we believed that the Earth was flat, but we have actually known for over 2,000 years that the Earth is round. Believe us when we say no one is trying to cover up that the Earth is flat. Why would we do that? The Earth is round and we love it.

Welcome to Astronotes

Hello, I’m Heather, welcoming you to Astronotes, the Armagh Observatory and Planetarium’s official blog. Here you will find the latest news and views from all those who work in our organisation, from the fascinating worlds of astronomy and space exploration. We hope you will come here to learn what is hot and exciting, profound or even weird from worlds beyond ours .
So that's the introduction out of the way, now on with the Universe!

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Armagh Observatory opened in 1790

Armagh Planetarium opened in 1968

Professor Louise Harra

Director of Armagh Observatory and Planetarium Michael Burton, on top of Mopra Rock in the Warrumbungles National Park of New South Wales. The 22m diameter Mopra radio telescope, star of the tale told here, lies below and behind him. (image credit: Michael Burton)